The present invention relates generally to vapor deposited films, and more particularly to system and method for producing nanocrystalline carbide/diamond-like carbon composite films having particular application to wear and friction reducing coatings.
Nanocomposites with microstructures comprising nanocrystalline grains in an amorphous matrix can produce unique mechanical and tribological properties. For example, in super-hard (50-55 GPa) nanocomposites previously reported ("Superhard Nanocrystalline W.sub.2 N/amorphous Si.sub.3 N.sub.4 Composite Materials," S. Veprek et al, J Vac Sci Tech A 14(1):46-50 (Jan./Feb. 1966); "A Concept for the Design of Novel Superhard Coatings," S. Veprek et al, Thin Solid Films 268:64-71 (1995)), plastic deformation was suppressed in order to maximize hardness, but the composites had characteristic brittleness undesirable for tribological applications where toughness and low friction coefficient are desired. Room temperature ductility in brittle ceramics was achieved by reducing grain size to nanometer levels ("Nanocrystalline Materials," H. Gleiter, in Progress In Materials Science 33:223-315 (1989); "Ceramics Ductile at Low Temperatures," J. Karch et al, Nature 330:556 (Dec. 1987)).
The invention solves or substantially reduces in critical importance problems with prior art composites and deposition methods by providing nanocrystalline carbide/diamond-like carbon (DLC) composite films and preparation method near room temperature. The composites are produced using a deposition technique that combines magnetron sputtering and pulsed laser ablation to produce plasma fluxes intersecting on a substrate surface to form metal, carbide and diamond-like materials. Composites produced according to the invention comprise 10 nm carbide crystallites encapsulated in a sp.sup.3 bonded amorphous DLC matrix having hardness of about 32 GPa and high plasticity at loads exceeding the elastic limit.
The invention has substantial application to production of wear and friction reducing composite films applied as coatings for protection against high contact loading in sliding and rolling. Composite films according to the invention exhibit high hardness and contact toughness, low (about 0.2) friction coefficient and low wear rates, and may adapt in use from hard to plastic depending on operating conditions, which substantially increase the wear life of bearings, shafts and other machine parts to which the films are applied as coatings.
It is therefore a principal object of the invention to provide improved nanocrystalline carbide/diamond-like carbon composites and method for producing the composites.
It is a further object of the invention to provide nanocrystalline carbide/diamond-like composite coatings for tribological applications.
It is a further object of the invention to provide low friction coatings having high contact toughness and low wear rates for systems operating under high contact stress such as in bearings, shafts and other precision turbine engine parts.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.